Machine components can become overloaded, for example, though failure of other components or as a result of the work that the machine is being called upon to do. It is desirable to provide a mechanism that can prevent damage due to such overloads.
Torque limiters are mechanical devices installed in a power driveline, for example between a driver such as motor or engine, and a driven part such as a pump, cutting head, rock crusher, or the like. Torque limiters can be particularly important in large high-power machinery in which failure of components can have very expensive consequences. Machinery for processing rocks such as rock crushers, tunnel boring machines, mining machines and the like are non-limiting examples of such heavy machinery. These machines are particularly vulnerable because the quantity and quality of feedstock that they are called upon to process may vary widely—causing the loads experienced by components of the machine to be somewhat unpredictable.
Torque limiters either slip at a pre-determined torque level or else allow the driving and driven parts to be temporarily separated at a pre-determined torque level, thereby preventing overload and failure of parts of the driveline.
There are several types of torque limiter in common use: shear pin, synchronous magnetic, ball detent, pawl and spring, and various styles of friction plate and clutch mechanisms, each type having advantages or disadvantages depending on the intended use.
One of the simplest torque limiting mechanisms is a shear pin. A shear pin is designed to be strong enough to transmit torque up to a design level and to fail at higher torques. The shear pin may be designed to fail at a level such that the delivered torque will not be enough to damage machine components downstream from the shear pin. While shear pins can be effective, simple to implement and relatively inexpensive, a disadvantage of the use of shear pins is that it can be time consuming to replace a failed shear pin. This is especially true where the shear pin is located in a part of the machine that is difficult to access. In large equipment the cost of downtime may be very large.
Various torque release couplings and torque-limiting clutches are described in the literature. For example, some of these are described in the following patent publications:                US 2011/0240313;        EP 1260753;        FR 2303205;        GB 933614;        GB 1293602;        U.S. Pat. No. 4,231,443;        U.S. Pat. No. 4,240,514;        U.S. Pat. No. 4,467,663;        U.S. Pat. No. 4,798,559;        U.S. Pat. No. 5,601,169; and,        U.S. Pat. No. 7,237,663.        
One type of torque limiting coupling is available from Lo-Rez Vibration Control Ltd. of Vancouver, Canada. In these couplings, driven and driver flanges are normally connected by an arrangement of safety elements which include balls that engage pockets. The safety elements employ a ball-detent arrangement. The driving balls are released from the pockets by a second set of balls specially arranged to “unlock” the main ball at a prescribed spring load, or equivalently, applied torque between the driver and driven parts. These couplings, while effective, are not designed to be remotely reset after an overload condition has occurred. This type of coupling can be reset by rotating the parts of the coupling into alignment and then tapping or hammering on the ends of rods that move when the coupling is released.
All of the couplings described above have various disadvantages for certain applications. For example, some of the couplings do not disengage input from output when an over-torque condition occurs but merely limit the torque delivered to the output. Some of the couplings cannot be remotely reset when an over-torque condition occurs. Some of the couplings provide no convenient way to adjust the maximum amount of torque that can be delivered.
Despite the variety of torque-limiting clutches and other mechanisms that are described in the literature, there remains a need for practical and cost-effective over-torque protection mechanisms. There is a particular need for such mechanisms that can be reset remotely after an over-torque condition has occurred. There is also a need for such systems which permit the maximum torque that the mechanisms can deliver before an over-torque condition is triggered to be adjusted.